(Not applicable)
This invention relates to the manufacture of golf club heads, particularly to the manufacture of wood-type or driver-type heads.
Wood-type heads are traditionally made from wood. However, with advances in materials, wood-type golf club heads have been made from various high-performance metals and other materials, such as titanium and fiber-reinforced plastics. Most club heads from fiber resin composite material are compression molded around relatively rigid molding cores. The majority of these finished club heads have a low quality composite, which is the result of difficulties in the process. To obtain a high quality composite in the club head using a rigid molding core, the core must be shaped very specifically and the uncured fiber resin material must be placed very precisely and systematically on the core to ensure that the proper amount of compaction occurs at all locations inside the golf club head.
Very few manufacturers have been willing to spend the money it takes to produce a high-quality composite in a golf club head. Instead, they often employ a process that combines an uncured resin with a heat-activated foaming agent around a foam core. Under low pressure, it expands and ensures almost full contact of the interior foam material to the outer composite material. The composite material in such heads is of a very low quality with high void content, low fiber content, and wrinkling of the reinforcing fibers.
In the few cases where the manufacturer has taken the time and expense to very accurately size and position all the materials going into the club head, other problems were encountered. The fiber resin material must be carefully positioned, one ply at a time, with intermediate compaction steps taken after every application of a few plies. This is very time-consuming and costly. Also the external shape design of such club heads is restricted to shapes which are more rounded in nature so the female tool applies a more uniform pressure to the exterior of the part. This imposes fairly serious shape design constraints. Most high performance club heads do not have these rounded shapes.
The club heads produced by the present invention do not suffer from these limitations. The high pressure exerted by the internal pressure bladder produces a very high quality product with low void content, high fiber volume laminate, better than the best costly compression molded club heads. The heads are also hollow which is a major benefit. Since the high compaction pressures are produced by the interior bladder, and not dependent on extremely precise sizing and placement of the uncured fiber resin material, the time and cost associated with laying up the uncured fiber resin material is reduced substantially. Also, since the compaction pressures are not dependent on the sizing and interaction of foam cores, the uncured fiber resin material, and the inside of the female tool, the club heads of the present invention have essentially no limitations in their shape.
A club head used with a particular shaft in a particular golf club type (i.e., a xe2x80x9cdriverxe2x80x9d which is also known as a xe2x80x9cnumber one woodxe2x80x9d, xe2x80x9cnumber two woodxe2x80x9d, etc.) will have an optimum weight chosen to maximize the playability of the club. Generally this can be stated as a particular club type having a given shaft length will need to have a predetermined set of mass properties to obtain an optimal configuration for playability and performance. These mass properties are the balance point and the swing weight (the center of gravity and mass moments of inertia). Therefore a given club head will have a set weight in its optimal design, not the lowest weight possible. Typically, for example, a xe2x80x9cdriverxe2x80x9d (xe2x80x9cnumber 1 woodxe2x80x9d) will have a club head weight of about 200 grams.
Generally, for most golfers using a given golf club type, larger club heads are more desirable and work better than smaller club heads, especially for wood-type heads. This benefit can be understood in the simplest sense by realizing that it is easier to hit the ball (not miss hitting it) with a larger club head. More precisely, it can be understood that a larger club head will generally have larger mass moments of inertia, and thus will be more stable and less prone to rotate on off-center hits during ball impact. Sometimes golf club heads are said to have xe2x80x9csweet spotsxe2x80x9d on the club head face. These areas are dependent on the mass properties of the club head, and also on the elastic properties of face. In general, the larger the size of face of the club, the larger the xe2x80x9csweet spot,xe2x80x9d which makes it easier for a golfer to strike the ball.
Given these design constraints on the club head, intelligently designed composite club heads do not use composite materials to decrease the club head weight, but to decrease the amount of material needed to provide the necessary strength and stiffness in the head. This has been termed herein xe2x80x9creducing the minimum structural weight.xe2x80x9d
Once the minimum amount of composite material needed for strength and stiffness has been obtained, additional material is then added to the head, either composite material or metallic material, to bring the head weight up to the desired optimal weight. Reducing the minimum structural weight maximizes the flexibility for location of this additional weight. The placement and location of the weight inside the club head have a very pronounced effect on the playability and performance of the club head. As mentioned, the final mass properties of the weighted club head, primarily the center of gravity and mass moments of inertia, have a large impact on the overall club performance. Reducing the minimum structural weight maximizes the tailoring which can be accomplished on mass properties, which improves club playability.
As an example, a lightweight titanium head might have 90% of its weight located as needed for structural performance. That means that 20 grams out of the 200 gram weight might be available to be placed where needed for mass properties. An equivalent composite carbon fiber epoxy head of the present invention would have 65% of its weight located as needed for structural performance, allowing 70 grams to be placed where needed for optimal mass properties.
As mentioned, larger club head size generally improves playability. Club head size is usually termed and measured as club head volume. The lower density of composite materials also allows for the manufacture of larger club heads which have better playability. The higher strength of club heads of the present invention also allows even larger club head volumes than previously offered by lower strength composite club heads. As explained in the detailed description of this invention, the method of the present invention produces high quality composite heads, in part because there is no one location in the head where several ply terminations occur simultaneously.
The construction methods disclosed herein produce very high performance composite club heads. Further refinement of all the various manufacturing steps for use in high volume production is anticipated. It is expected that it will be recognized by those skilled in the art that the many variations possible without departing from the scope and spirit of this invention.
One of the methods for forming fiber-reinforced composite club heads involves molding around a relatively rigid molding core, which may or may not be removed after cure. An example of such a method is disclosed in U.S. Pat. No. 4,581,190 to Nagamoto et al. The Nagamoto et al. reference discloses a process for making a club head where a fibrous bag of reinforcing fiber is placed over a rigid molding core. The fibrous bag, which in the patent drawings appears to resemble a paper sack, is impregnated with plastic. The plastic is cured by applying heat under external pressure, which presses the impregnated bag against the core during molding.
Nagamoto et al. discloses another method conceptually and describes it without any detail or drawings. In this method, the loosely arranged bag of fibrous reinforcing material is placed around a second bag of impervious material (vinyl chloride). Both bags are placed into a mold and the impervious bag is inflated by introducing air vapor or liquid (e.g., oil) under pressure to press the bag of reinforcing material against the wall of the cavity of the mold.
The Nagamoto et al. methods illustrate two approaches in the prior art for making club heads. The first approach involves forming impregnated fibers around a rigid molding core and curing the fibers by externally pressing the impregnated fibers against the rigid core. This class of methods has several disadvantages. The main one being the molding core usually remains in the interior of the club after molding. Nagamoto et al. mentions this xe2x80x9cinconveniencexe2x80x9d on line 35 column 4. The molding core is usually left in the head as permanent component of the head, or can sometimes be removed. To remove the core, it has been proposed to use various removable materials for the core such as various lost-mold compounds, low-melting salts or metals, waxes, and plastic foams that can be dissolved by a solvent. The difficulty is that the core material must be strong and heat-resistant to withstand the molding conditions, since the core must support the cure temperature and the compression of the fiber bag against the core. However, strength and heat resistance are counter to properties that allow easy removal of the core. Consequently, the core materials that have high temperature and strength properties for molding are either expensive, are hazardous materials and/or difficult to handle (such as low-temperature-melting salts or metals), or must be removed by toxic solvents. In addition, for many core materials, the molding pressure and temperature are limited by the physical properties of the core. For example, polystyrene foam cannot withstand higher temperature and higher pressures, which precludes its use in making high-compression composite materials. For high-pressure compression, only the higher strength core materials can be used, which usually bring about increased problems of safety, cost, and difficulty in handling or removal. The higher strength core materials, such as wax and low melt metal alloys, have substantial thermal mass, generally on the order of several times the composite material being molded. This high thermal mass is also on the inside of the head, with almost all composite materials having relatively high thermal resistance through the thickness of the laminate. The combination of these effects effectively lengthens the molding times considerably, because of the extra time required to heat the entire head and core structure. Decreasing molding cycle time by a factor of 2 or 4 would have a dramatic effect on the cost effectiveness and economic feasibility of a head manufacturing process.
The second approach in the Nagamoto et al. patent (disclosed at col. 4, lines 35 to 53) describes the second general approach for forming composite material heads, and avoids the problem of a core remaining in the molded article by eliminating the molding core. The process involves placing a bag of loosely arranged impregnated fibers around an impervious bag of vinyl chloride, which is inflated to press the impregnated fibers against the cavity walls in the mold. Since there is no molding core around which to place the fiber bag, the bag of fibers and the inflatable bag are only loosely placed together. When the bag is inflated, there is a large amount of movement of the fibers as the bag expands and moves the fibers against the cavity walls, and the fibers cannot be located with much precision. This causes the club head to have unpredictable fiber orientations because of the imprecision of the final fiber placement. In addition, the use of plies over only a portion of the club head or plies in a specific fiber orientation is precluded, because the reinforcing fibers must be in the form of a bag. It would be very difficult or nearly impossible, for example, to optimize the design of the club head by placement of one or more plies in selected portions of the club head to increase strength and stiffness in the portion. During expansion of the impervious bag, the surrounding fiber bag would tend to move significantly from their original position, and a specific placement of the fibers would be difficult due to the looseness of the initial placement of the bag
The second Nagamoto et al. process does not describe any means for introducing a pressurized fluid or gas into the bag, or specific means for constructing the impervious bag and the raw material form used, or the means for attaching a pressure delivery source to the bag inside the mold, or the anticipated or required temperature and pressure capability of the impervious bag system. There is no indication of pressure levels that could be applied to a vinyl chloride impervious bag, and what molding temperatures could be. If the temperature increase of the gas initially in the bag provides the pressure, which would be the simplest approach and is disclosed by U.S. Pat. No. 4,575,447 to Hariguchi line 65, column 1, there would be several limitations. The pressures would be restricted to very low compaction pressures, and such pressures would not be controllable independently from the mold/part temperature.
An alternate process to the Nagamoto et al. inflatable bag molding process is disclosed in U.S. Pat. No. 4,575,447 to Hariguchi. In the Hariguchi process an impervious bag is manufactured as a hollow core of a material that is rigid at room temperature. The rigid core is shaped similar to the final shape. Impregnated fibers are placed around the hollow core and placed in a female mold. During molding, the core softens under heat of the molding, which then can be expanded by pressurizing the core. This presses the impregnated fibers against the mold. The pressure inside the core can be provided by thermal expansion of air sealed inside the head, or by introduction of a pressurized medium. The problem with this approach is that the hollow core is limited to rigid materials that can be softened and inflated during molding. In addition, the softened hollow core becomes attached and incorporated into the interior of the club head. Thus, the inflatable core remains as a permanent part of the club head. The thermoplastic core, which for a material like polyethylene, would be limited to low pressures at the cure temperatures that are typically used in composite sporting goods manufacturing. Since the process relies on a rigid material that softens at a particular temperature, the entire process would have to be designed around this temperature, regardless of its suitability for processing, i.e., the curing of the composite. Application of pressure to the rigid core below the softening temperature would not supply any compaction pressure to the composite because of the core""s rigidity. It is desirable to apply compaction pressure over a wide range of temperatures during the cure, even at near room temperature conditions when the mold is just closed. If thermal expansion of the air trapped inside the core is used for pressure, the process would be limited to relatively low pressures from the core.
In summary, prior-art systems, suffer from one or more of the following problems:
(1) Significant residue remains in the interior of the molded club, either
(a) an entire molding core that is hard to remove, or is otherwise a toxic or difficult material that requires special handling, or
(b) an inflatable bag or core remains and becomes incorporated with the club head material and cannot be removed;
(2) Low molding pressures are used because of the inherent weakness of the inflatable materials being used and their inability to retain high pressure under the high molding temperatures. Weakness in the finished club head results from low compaction of the fibers produced by low molding pressures, which causes a lower fraction of structural fiber in the composite part relative to the resin;
(3) Weaknesses and unpredictable wall thicknesses at critical locations occur in the final molded part due to movement of the plies during molding (See, for example, U.S. Pat. No. 4,575,447 to Hariguchi line 45, column 1) or inaccurate placement of plies.
(4) The processing pressure is apparently dependent upon the temperature for some of the processes. This leads to less than optimal processing conditions.
It is, therefore, an object of the invention to provide a process for the manufacture of composite golf club heads.
It is further an object of the invention to provide a process that allows for accurate placement of the plies of fibrous material in the final molded part.
It is further an object of the invention to provide a process wherein there is little or no residue from the molding process remaining in the interior of the club head.
It is further an object of the invention to provide a process for the manufacture of a club head that allows for high pressure molding of the composite, to form a high fiber volume composite laminate with low void content.
It is further an object of the invention to provide all these aspects listed above, in a golf club head which is an almost entirely closed shape, which can be made with only a small opening in the as molded state, from which all the interior molding features are easily removed after molding.
Further objects of the invention will become evident in the description below.
An embodiment of the invention is a process which has the advantages of both a relatively rigid molding core processes and an inflatable bag process, but avoids major disadvantages of each. The initial preform of uncured impregnated fiber is formed around a mandrel core or forming core surrounded by an inflatable bladder, so that the preform is dimensioned near to the final shape and does not require significant movement of fibers to conform to a mold cavity. The mandrel core is used only for formation of the uncured preform of uncured resin composite, and it is not used in the actual molding process. Therefore, the strength and heat resistance of the mandrel core is not critical.
Before the impregnated fibers are placed around a core, the core is placed in an inflatable, fluid-impervious bladder. During molding, the bladder is inflated to press the impregnated fibers against female tooling. Since the core does not have to withstand the pressure and temperature molding conditions, it may be made of materials that are structurally weak and unable to withstand elevated molding pressures and temperatures. This allows the use of materials that are completely unsuitable as rigid molding cores in prior-art systems. Thus, a material can be used, such as starch foam, that can be easily removed by dissolving with a readily available and non-toxic solvent, water. Previously such materials have not been used in composite processes because they do not have the strength to withstand molding conditions. However, since the mandrel core is only used for laying up the part, it does not function as a support or molding core during the compressing and heating during molding. For this reason, a molding core material may be chosen that may or may not withstand the high temperature and pressure conditions of molding.
After molding, in the preferred embodiment of the invention, the core can then be easily removed merely by injecting water into the inflation bladder inside the molded part to disintegrate or dissolve the core sufficiently to allow it to be washed out and allow subsequent removal of the bladder. No special handling or disposal is required, which would be the case for removal of molding cores of liquid salts or plastics dissolvable only in organic solvents. The bladder is made of a heat resistant plastic that does not soften or react with the interior of the interior of the molding part. Thus, it can become separated therefrom and be easily removed, along with any small residue of the mandrel core that may be within the bladder.
Additionally, in an embodiment of this invention, the bladder is of a thin film, that is of only a small volume of material. The film bladder can then be removed by pulling out of a small opening in the molded part. Additionally the thin film bladder itself can be a soluble plastic, e.g., water soluble, such as poly vinyl alcohol (PVA) film. The use of easily soluble bladder films is advantageous where extremely small openings are used for inflation during molding and removal subsequently. Soluble films are also used if molding of complex features on the inside of the part might inhibit removal of the bladder. Such complexities might involve cocured features inside the head.